"Stop Leak" Coolant Additive. Which one?

[BTR]

I've repaired as many coolant leaks as I can find. However, somewhere, there's still have a very-small leak... very small. What "Stop Leak" additives have you had success with? Which ones should I stay away from? Thanks for your help!

 

[koda2000]

K-Seal worked great for me. If it doesn't stop the leak nothing will IMO. I shake it up real well and add it directly to the radiator. It's stopped my leaks in minutes.

 

[Mr. Alligator]

K-Seal worked great for me...

@koda2000 How do you know/Trust that whatever will stop the leak won’t clog up other things in the cooling system? .... Maybe I am just paranoid about these products. I do appreciate your opinion.

Thanks.

 

[koda2000]

@koda2000 How do you know/Trust that whatever will stop the leak won’t clog up other things in the cooling system? .... Maybe I am just paranoid about these products. I do appreciate your opinion.

Thanks.

Because K-Seal says it will not clog anything right on the bottle and from reading customer reviews. K-Seal is not a sticky kind of sealant. It looks like cookie crumbs in chocolate milk and it remains active in the system to seal future leaks. I'm not much for "cures in a bottle" but I can testify the this stuff really works.

Note: If you have a radiator tank seal leaking, don't bother with sealants. Just replace the radiator.

 

[donalds]

K -seal
I used it and it works permanently

 

[1997XLTRollover]

K-Seal. It stays liquid in the system. Good stuff.

 

[BTR]

My leak is definitely not in the radiator (replaced recently; no leaks found currently). Additionally, there's no white smoke coming from the exhaust (never has been; not now). And there's no smell of coolant in the cabin (heater core). Thanks for the recommendation to use K-Seal. After I flush the system, I'll add a bottle along with new coolant.

 

[koda2000]

K -seal
I used it and it works permanently

Yes, it is considered a "permanent repair" but I've found that when I've replaced my coolant I've had to toss in another bottle. When I tore down my SOHC engine I found no residue remained on anything. I've read where others here have even had success on OHV V6 cracked heads using K-Seal. Excellent stuff for small leaks. It even worked for a gusher of a W/P leak on my old 5.0L XLT. I think it would even be a good idea to add it to a non-leaking cooling system as preventative maintenance as it remains active in the cooling system.

 

[8TZX]

Thumbs up for the K-Seal. I had to replace my radiator and thermostat housing in my 99 5.0 three months ago. I thought this stopped the leaks. I still had one very small leak located at possibly the water pump or timing cover. I added one bottle of K-Seal to the coolant recovery tank. It's been 3 months and no leaks.

 

[bmdubya1198]

Good to know about K-seal actually being a good option. I’m glad to see that someone has actually torn into the engine so see that there’s no residue.
Someone had previously used a stop leak on one of my Volvos, and even after a total cooling system overhaul and flush, there are still metallic flakes from it that occasionally show up.

Anyway, normally I would urge against using a stop leak unless it’s a last resort effort on an engine that’s in questionable condition. I would recommend pressure testing the cooling system and trying to find a drip. Check all hoses, water pump, thermostat, etc. as well as the heater core.
That said, if this K-seal stuff is a proven product, it may be worth a try. I have never used it, in fact the only stop leak I’ve ever used is Lucas power steering stop leak.

 

[cober]

I use "high gear". Worked for me and didn't clogged heater.

 

[Gary Crist]

Will an intake manifold leak do what you are experiencing?

 

[masospaghetti]

ACDelco "seal tabs" are another good option, they were added to some GM vehicles as a factory fill to resolve porosity issues.

I would also encourage you to use a coolant leak tester kit to find small leaks. It allows you to pressurize the system when cold and without the engine running. I've found many small leaks this way that would be impossible to find otherwise. Autozone will loan them out for free.

 

[96eb96]

I've repaired as many coolant leaks as I can find. However, somewhere, there's still have a very-small leak... very small. What "Stop Leak" additives have you had success with? Which ones should I stay away from? Thanks for your help!

k-seal still holds for me! I had to drop the coolant, I didn't know it was even there.

 

[vanman9]

I chased a minor leak for a long time. Turns out it was one of the 2 white plastic 90 degree elbows connecting the heater hose fitting hose to the main hose. Went to the auto parts store expecting to have them order it and the guy says how many do you need?? Turns out it's a common problem and he has a big box of them...Just cracked didn't even leak all the time.

 

[icecoldbear62]

Have you done a pressure test on the whole system ???
that’s the best way to find the leak in your system if you don’t find a leak then you may have a weak head gasket that is running out or burning off in the head that type of head gasket problem won’t give you white smoke till the gasket finally lets go all together !!!
Have seen it in the 4.0,
3.0,and the 5.0 as well as the 4.6 and 5.4 never seen it on a 5.8 !!!
Putting any kind of sealer in the cooling system can lead you to big HEAD ACKES DOWN THE ROAD TAKE MY WORD FOR IT !!!
Been there done that and for what would have been a couple head gaskets and maybe having the head trued couple hundred in parts if you do it your self !! Than no heat all of a sudden and even a blown motor because of blocked coolant jackets in the engine !!! Add some die to coolant and do a full system pressure test and just look for what ever color die you added to the system !!
Either way good luck !!!!!!

 

[donalds]

Ever taken apart a 4.0 that's the easy part
Stop leak yea will clog coolant passages
K seal not seen it yet it's great stuff
Imo

 

[bryansr]

FYI, the "very small leak" that I couldn't find on my 98 SOHC ended up being the lower thermostat housing.
When it finally failed due to heat/age two yrs ago, the small nipple on top broke off and it blew out a lot of coolant.

 

[donalds]

Did you replace it with a metal one

 

[UtahX]

K-Seal works for me, great stuff.